Previous to its recognition as an AIDS-associated disease (1), Kaposi's sarcoma (KS), initially described in three fatal cases of sarcoma by Mortiz Kaposi in 1872, was primarily found in elderly men (over 50 years of age) of Eastern European, Mediterranean, or African descent. The clinical, histopathological and epidemiological aspects of the endemic or classical form of KS found in these populations have been studied extensively. In African patients, KS generally presents as either an indolent disease in elderly people or an aggressive infiltrative or nodular disease in young individuals. The latter has many features in common with those observed in patients with HIV-1 infection. Kaposi's sarcoma, with a pattern similar to that found in AIDS patients, also occurs at an increased frequency in transplant recipients and in patients receiving immunosuppressive therapy. Histological observations have shown that KS lesions contain proliferating spindle cells (probably of lymphatic origin), as well as other endothelial cells, fibroblasts, erythrocytes, and infiltrating leukocytes. A very important feature of the KS lesion is the presence of extensive neovascularization.
An unusual feature of KS is its appearance as a multi-focal neoplastic lesion. This suggests a polyclonal origin rather than a classical malignancy involving an initial clonal cell transformation followed by metastasis. Despite abundant epidemiological data, the etiology and pathogenesis of KS is still unknown. Genetic factors (such as HLA patterns), viral involvement (such as Epstein-Barr virus and human cytomegalovirus), and chemical effects (such as amyl nitrate usage), acting independently or in concert, have all been suggested as contributing elements. However, none of these factors have been convincingly linked to the cause or pathogenesis of any form of KS. In contrast, there is a clear correlation between HIV-1 infection and the new aggressive form of epidemic KS, while other forms of KS have no HIV-1 association. However, HIV-1 is apparently not directly involved in the origin of this neoplasm by a direct multi-focal transformation of progenitor cells, since HIV-1 nucleotide sequences have not been detected in the DNA of KS tissues. Moreover, the greater incidence of KS in HIV-1-infected homosexual males compared to other groups at risk for AIDS has lead to the suggestion that other environmental factors or possibly another virus (with HIV-1) might be involved in the initiation and/or maintenance of AIDS-KS.